An acoustic guitar bridge is held in place with glue and occasionally also have screws with bolts "helping" to hold the bridge in place. Over time the bridge will likely begin to loosen and a small gap will appear along the back edge. Every time I work on an acoustic guitar it's something I'll check because the longer it's ignored the worse the problem becomes. At the very least I can discuss it with the customer so they aware of the problem and can keep on eye on it.
If the problem isn't discovered or it is ignored for too long the bridge itself can warp making the process of fixing it even more expensive. In really bad instances the stress created on the bridge pins can actually crack the top of the guitar and then the "fix" is even more involved and therefore more expensive. The moral of the story here is...get it fixed as soon as you're able to.
On most guitars the bridge is glued to the wood as one would expect. However some of todays acoustic guitars (especially affordable imports) have the bridge glued to the finish. It is pretty common to see these bridges begin to lift far sooner than a bridge glued "wood to wood". Sometimes I wonder if the affordable imported instruments have a warranty that is just a few weeks shorter than the life expectancy of the glue holding the bridge in place. It is certainly understandable to be frustrated that a guitar (only a couple of years old) would need this work but it's the reality of mass produced affordable instruments. Ironically the less expensive the guitar was new the more expensive it is to fix.
Here is a summary of the process but remember, each situation is different so the process will vary accordingly...
- Heat and carefully remove the bridge.
- Clean the surface of the bridge carefully removing any top wood that came off with it.
- Any top wood that can be removed from the bridge is reglued to the top before fitting begins.
- Bridges that have warped over time will often benefit from some "flattening" techniques.
- The top surface will be cleaned and prepped for the bridge.
- Here's where a less expensive guitar gets more expensive to fix!
- Whenever possible I try remove the thick catalyzed finish so the new glue joint is wood to wood.
- Guitars with plywood top will often crack and start to delaminate under the bridge but it isn't always possible to know that before work begins.
- After carefully fitting the bridge to the top I'll make any clamping cauls needed and do a dry run to make sure the setup will work.
- I then apply glue to both surfaces and clamp the bridge in place cleaning up all the glue squeeze out around the bridge.
- The instrument will be left overnight with clamps and at least 24 hours before stringing it back up to pitch.
- The bridge pin holes need to be cleaned up and pins fit properly.
- Restring, tune to pitch and whenever possible observe for a few days.
I'm proud to say none of the bridge reglues I've done have "failed" prematurely. It isn't to say the bridge will never need to be reglued again but often times the time I take fitting the bridge to the top was as good or better than when the guitar was originally made.